[oris8] 24.11.26

oris8/102_binary-tree-level-order-traversal.js

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+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ *
+ * 102 / Binary Tree Level Order Traversal / Medium / 12m 8s
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var levelOrder = function (root) {
+  if (!root) return [];
+
+  const result = [];
+  const queue = [root];
+
+  while (queue.length > 0) {
+    const levelSize = queue.length;
+    const currentLevel = [];
+
+    for (let i = 0; i < levelSize; i++) {
+      const node = queue.shift();
+      currentLevel.push(node.val);
+
+      if (node.left) queue.push(node.left);
+      if (node.right) queue.push(node.right);
+    }
+
+    result.push(currentLevel);
+  }
+
+  return result;
+};
+
+// var levelOrder = function(root) {
+//     const result = [];
+
+//     const traverse = (node, level) => {
+//         if (!node) return;
+//         if (result.length === level) {
+//             result.push([]); // 새로운 레벨 생성
+//         }
+//         result[level].push(node.val); // 현재 레벨에 값 추가
+//         traverse(node.left, level + 1); // 왼쪽 자식 탐색
+//         traverse(node.right, level + 1); // 오른쪽 자식 탐색
+//     };
+
+//     traverse(root, 0);
+//     return result;
+// };

oris8/128_longest-consecutive-sequence.js

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+/**
+ *
+ * 128. Longest Consecutive Sequence
+ * Medium
+ * Topics
+ * Companies
+ * Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
+ *
+ * You must write an algorithm that runs in O(n) time.
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function (nums) {
+  // 중복되는 요소 허용, 빈 배열 허용
+  if (nums.length === 0) return 0;
+
+  const set = new Set(nums);
+  const sortedSet = Array.from(set).sort((a, b) => a - b);
+
+  let maxSequenceLength = 1;
+  let currentSequence = [sortedSet[0]];
+
+  for (let i = 1; i < sortedSet.length; i++) {
+    const last = currentSequence.pop();
+    if (last + 1 === sortedSet[i]) {
+      currentSequence.push(last);
+      currentSequence.push(sortedSet[i]);
+    } else {
+      currentSequence = [sortedSet[i]];
+    }
+    maxSequenceLength = Math.max(maxSequenceLength, currentSequence.length);
+  }
+
+  return maxSequenceLength;
+};

oris8/150_evaluate-reverse-polish-notation.js

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+/**
+ *
+ * 150 / Evaluate Reverse Polish Notation / Medium / 36m 44s
+ *
+ * @param {string[]} tokens
+ * @return {number}
+ */
+var evalRPN = function (tokens) {
+  const operators = {
+    "+": (a, b) => a + b,
+    "-": (a, b) => a - b,
+    "*": (a, b) => a * b,
+    "/": (a, b) => Math.trunc(a / b),
+  };
+
+  const stack = [];
+
+  for (const token of tokens) {
+    if (operators?.[token]) {
+      const b = stack.pop();
+      const a = stack.pop();
+      stack.push(operators[token](a, b));
+    } else {
+      stack.push(+token);
+    }
+  }
+
+  return stack.pop();
+};

oris8/207_course-schedule.js

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+// 207 / Course Schedule / Medium / -
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+var canFinish = function (numCourses, prerequisites) {
+  const graph = new Map();
+
+  // 그래프 생성
+  for (let i = 0; i < numCourses; i++) {
+    graph.set(i, []);
+  }
+
+  for (const [course, prereq] of prerequisites) {
+    graph.get(prereq).push(course);
+  }
+
+  // 방문 상태 관리
+  const visited = new Set(); // 현재 DFS 방문 중인 노드
+  const completed = new Set(); // 이미 처리 완료된 노드
+
+  // 사이클 탐지 함수
+  const dfs = (course) => {
+    if (visited.has(course)) return false; // 사이클 발견
+    if (completed.has(course)) return true; // 이미 확인된 경우
+
+    visited.add(course); // 현재 노드 방문 중
+    for (const nextCourse of graph.get(course)) {
+      if (!dfs(nextCourse)) return false; // 다음 코스에서 사이클 발견
+    }
+    visited.delete(course); // 탐색 완료 후 제거
+    completed.add(course); // 완료된 노드로 기록
+
+    return true;
+  };
+
+  // 각 강좌에 대해 DFS 실행
+  for (let i = 0; i < numCourses; i++) {
+    if (!dfs(i)) return false; // 사이클이 존재하면 false 반환
+  }
+
+  return true; // 모든 강좌를 완료할 수 있음
+};

oris8/208_implement-trie-prefix-tree.js

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+/**
+ * 208. Implement Trie (Prefix Tree)
+Medium
+Topics
+Companies
+A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.
+
+Implement the Trie class:
+
+Trie() Initializes the trie object.
+void insert(String word) Inserts the string word into the trie.
+boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
+boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.
+
+1 <= word.length, prefix.length <= 2000
+word and prefix consist only of lowercase English letters.
+At most 3 * 104 calls in total will be made to insert, search, and startsWith.
+ */
+
+// var Trie = function() {
+//     node
+// };
+
+class TrieNode {
+  constructor() {
+    this.children = {};
+    this.words = new Set();
+  }
+}
+
+class Trie {
+  constructor() {
+    this.root = new TrieNode();
+  }
+
+  traverse(word) {
+    let node = this.root;
+    for (let char of word) {
+      node = node.children[char];
+      if (!node) return null;
+    }
+    return node;
+  }
+}
+
+/**
+ * @param {string} word
+ * @return {void}
+ */
+Trie.prototype.insert = function (word) {
+  let node = this.root;
+  for (const char of word) {
+    if (!node.children[char]) {
+      node.children[char] = new TrieNode();
+    }
+    node = node.children[char];
+  }
+  node.words.add(word);
+};
+
+/**
+ * @param {string} word
+ * @return {boolean}
+ */
+Trie.prototype.search = function (word) {
+  let node = this.traverse(word);
+  return !!node && node.words.has(word);
+};
+
+/**
+ * @param {string} prefix
+ * @return {boolean}
+ */
+Trie.prototype.startsWith = function (prefix) {
+  let node = this.traverse(prefix);
+  return !!node;
+};
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * var obj = new Trie()
+ * obj.insert(word)
+ * var param_2 = obj.search(word)
+ * var param_3 = obj.startsWith(prefix)
+ */

oris8/213_house-robber-ii.js

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+/**
+ * 213 / House Robber II / Medium / 13m 27s
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var rob = function (nums) {
+  // T(n) = Math.max(T(n-1), T(n-2) + n)
+  if (nums.length <= 2) return Math.max(nums[0], nums?.[1] || 0);
+
+  const results = [nums[0], Math.max(nums[0], nums[1])];
+  const not1results = [0, nums[1]];
+  for (let i = 2; i < nums.length; i++) {
+    results[i] = Math.max(results[i - 1], results[i - 2] + nums[i]);
+    not1results[i] = Math.max(not1results[i - 1], not1results[i - 2] + nums[i]);
+  }
+
+  return Math.max(results[nums.length - 2], not1results[nums.length - 1]);
+};

oris8/226_invert-binary-tree.js

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+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var invertTree = function (root) {
+  if (root) {
+    [root.right, root.left] = [invertTree(root.left), invertTree(root.right)];
+  }
+  //   if (!root) return null;
+  //   [root.left, root.right] = [invertTree(root.right), invertTree(root.left)];
+
+  return root;
+};

oris8/371_sum-of-two-integers.js

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+/**
+ * 371. Sum of Two Integers
+ * Medium
+ *
+ * Given two integers a and b, return the sum of the two integers without using the operators + and -.
+ *
+ * -1000 <= a, b <= 1000
+ *
+ * @param {number} a
+ * @param {number} b
+ * @return {number}
+ */
+var getSum = function (a, b) {
+  // 비트 연산 사용
+  /**
+   *
+   *  XOR  :각 비트를 비교하여, 두 비트가 서로 다르면 1을 반환하고, 같으면 0을 반환
+   *        === carry(올림)를 무시한 덧셈과 동일한 결과
+   *
+   *  AND  :두 비트가 모두 1인 경우
+   *
+   *  자리올림은 두 비트가 모두 1일때 발생하므로 AND 연산을 통해서 이를 확인하고, 두 비트가 모두 1일 경우 자리올림 수행 (<<)
+   *
+   */
+
+  return b === 0 ? a : getSum(a ^ b, (a & b) << 1);
+};

oris8/543_diameter-of-binary-tree.js

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+/**
+ * 
+ * 543. Diameter of Binary Tree
+Easy
+Topics
+Companies
+Given the root of a binary tree, return the length of the diameter of the tree.
+
+The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.
+
+The length of a path between two nodes is represented by the number of edges between them.
+
+The number of nodes in the tree is in the range [1, 104].
+-100 <= Node.val <= 100
+
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var diameterOfBinaryTree = function (root) {
+  let maxDiameter = 0;
+  const getBinaryTreeHeight = (node) => {
+    if (!node) return 0;
+
+    // 현재 노드부터 높이를 재귀적으로 계산
+    const right = getBinaryTreeHeight(node.right);
+    const left = getBinaryTreeHeight(node.left);
+
+    maxDiameter = Math.max(maxDiameter, right + left);
+
+    // 현재 노드를 포함하기 위해 + 1
+    return Math.max(right, left) + 1;
+  };
+
+  getBinaryTreeHeight(root);
+  return maxDiameter;
+};